The present invention relates to a system and method for monitoring material levels in various types of material containment vessels and structures and, more particularly, to such a system and method in which material levels in a number of such containment structures are all monitored using micropower impulse radar probes communicated to a remotely located central, computer.
Recent environmental concerns with underground fuel storage tanks have led the Environmental Protection Agency to create strict monitoring rules for gasoline service stations and other users of such tanks. Compliance with these regulations, which can require accuracy within xe2x85x9 inch of liquid level and must detect leakage rates of as little as 0.1 gal/hr. or less, can be an expensive and time consuming activity for a small business such as a service station. In an effort to alleviate this burden, a number of companies have developed systems for monitoring underground storage tanks for leakage compliance. In addition, some of these systems use the data collected for inventory management services as well. Examples of leak detection systems are found in U.S. Pat. No. 4,852,054 to John Mastrandrea; U.S. Pat. No. 5,075,877 to Allan Jacob; U.S. Pat. No. 5,297,423 to Jerome Keating, et al.; U.S. Pat. No. 5,363,093 to Barry Williams et al.; U.S. Pat. No. 5,400,253 to Paul O""Connor; U.S. Pat. No. 5,471,867 to John Tuma et al.; and U.S. Pat. No. 5,757,664 to Warren Rogers, et al. These prior art systems all require complex liquid level sensors which are hardwired to monitoring computers on site. This presents a number of problems. Typically, installation of such liquid level sensors requires the tank top to be accessed, which means tearing up concrete or asphalt surfaces covering the tank. The cables connecting the liquid level sensors to the monitoring computer are usually run beneath the road surface, which also requires the concrete or asphalt to be cut. Such probes usually must be installed in risers other than the fill riser, which can require expensive tank modifications. Many prior art systems require the installation of additional sensors such as temperature and/or pressure probes to detect fuel temperature and internal tank pressure as variables in computing liquid volume. Finally, many prior art centralized systems require a dedicated telephone line from service station to central monitoring computer, which also adds to the expense.
It is clear, then, that an improved underground storage tank monitoring system and method is needed. Such a system and method should avoid the above-mentioned problems of the prior art and should provide reliable monitoring at an economical price. Additionally, there is a need for improved material level monitoring of many types of wet and dry flowable materials stored. in a variety of underground and above-ground tanks and other types of containers and containment vessels and structures.
The present invention is a material level monitoring system and method which uses a micropower impulse radar transmitter/receiver as a liquid level probe. Technical details for the micropower impulse radar probes are found in U.S. Pat. No. 5,609,059, entitled xe2x80x9cElectronic Multi-Purpose Material Level Sensorxe2x80x9d and U.S. Pat. No. 5,610,611, entitled xe2x80x9cHigh Accuracy Electronic Materials Level Sensorxe2x80x9d, which patents are incorporated herein by reference. Such a probe is positioned into each containment structures. The micropower impulse radar probes use a flexible waveguide which extends downward toward the bottom of the containment structure. The probe radiates a micropower radar impulse down the waveguide, to reflect off of the material surface and return to the probe. The time lapse between emission and reception of the impulse by the micropower impulse radar probe is measured and a distance to the material surface, and thus a material level, can be calculated therefrom. If there are multiple layers of material within the containment structure, such as wet and dry layers, immiscible liquids such as oil and water, or the like, a secondary or tertiary reflection of an impulse can detect the level of the interface between the layers, relative to the upper surface. By this means, some types of contamination of a material within a containment structure can be detected. The containment s structures with which the material monitoring systems of the present invention are applicable include wide variety of in-ground, above-ground, and underground structures for holding, storing, or channeling a wide variety of flowable materials including liquid, granular, and particulate materials.
In an exemplary embodiment of the material level monitoring system, each micropower impulse radar probe is connected to a dedicated, low power, spread spectrum transmitter which collects level and status information from the probe, encodes and transmits it to a matching spread spectrum receiver nearby. The receiver converts the spread spectrum encoded signals into data signals and forwards them to a processor, to which is connected a modem and a back-up battery power source. The processor stores the material level information for later transmission to a central monitoring site via the modem. A data entry keyboard may be provided for entering material intentionally stored in the containment structure or withdrawn therefrom, for example where the present invention is used for detecting leakage of the material. Unlike many other systems which periodically poll the monitoring station from the central monitoring site, the inventive system does not require a dedicated telephone line for implementation since the data transmission is initiated from the service station only during regular reporting times or when an abnormal condition occurs.
In addition to spread spectrum encoded radio communication links, the present invention contemplates other modes of communicating material level data from the micropower impulse radar probe assemblies to intermediate material level monitoring stations and central monitoring stations. For example, fiber optic, infrared, satellite, direct laser, and other communication media are contemplated in the present invention.
The material level data derived from the apparatus and methods of the present invention can be used for a number of purposes. Leakage of a stored material or degree of contamination of a stored material may be detected and alerts generated in response to such detection. Material levels can be monitored for accounting and inventory control purposes and to generate replenishment actions in response to depletion of the stored material, such as controlling refilling, scheduling delivery, or the like. Material level detection using the present invention can be used for certain aspects of process control, such as to control a valve to replenish a vessel storing a process material. The system of the present invention can be used for flood detection in natural and artificial waterways and bodies of water and for generating alerts and responses to such flooding, such as the activation of pumps.
The objects and advantages of the invention include: providing improved apparatus and methods for monitoring and reporting levels of materials in various kinds of containment vessels and structures; providing such material level monitoring apparatus and methods employing micropower impulse radar probes for detecting relative heights or levels of a wide variety of flowable materials, such as liquids, granular and particulate materials, and the like; providing such apparatus and methods for monitoring material levels within above ground tanks, underground tanks, process vessels, silos, and natural and artificial bodies of water and other fluids such as ponds, lakes, streams, canals, and the like; providing an exemplary embodiment of a material level monitoring system in the form of a fuel storage tank monitoring system and method in which a number of different underground storage tanks can be monitored efficiently from a central monitoring site; providing such a storage tank monitoring system and method in which a micropower impulse radar probe is inserted into each tank via a riser, connected to a spread spectrum transmitter positioned in a manhole containing the riser, which transmitter transmits liquid level information to a remote receiver; providing such a storage tank monitoring system and method in which a special installation system allows the micropower impulse radar probes to be inserted via the fill riser of an existing tank where no monitor riser is available; providing such a storage tank monitoring system and method which uses liquid levels, as measured by the micropower impulse radar probes, along with quantities of fuel dispensed from the tank and fuel replaced in the tank to calculate leak rates and, optionally, perform inventory control; providing such a material monitoring system and method which is particularly economical to install and implement as compared to existing systems; and providing such material level monitoring system and method which is particularly well suited for its intended purpose.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.